Liquid Crystal Display Device

ABSTRACT

A liquid crystal display device includes first and second substrates with a liquid crystal layer therebetween, a plurality of gate signal lines made of metal and a plurality of drain signal lines made of metal, wherein the gate signal line and the drain signal line have a first overlapping region, and a plurality of counter voltage signal lines, wherein the counter voltage signal line and the drain signal line have a second overlapping region. A plurality of pixel regions are defined by neighboring gate signal lines and drain signal lines, and a pixel electrode is formed on the first substrate in each pixel region. A thin film transistor having a semiconductor layer is formed on the gate signal line, and the semiconductor layer at least overlaps with the drain signal line at the first overlapping region and the second overlapping region.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of application Ser. No. 11/002,508,filed Dec. 2, 2004, which is a continuation of application Ser. No.10/939,941, filed Sep. 14, 2004, which is a continuation of applicationSer. No. 10/070,538, filed Mar. 7, 2002, the subject matter of which isincorporated by reference herein and is a 371 of PCT/JP00/06009, filedSep. 5, 2000.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device, and,more particularly, to a so-called “lateral electric field type” liquidcrystal display device.

BACKGROUND OF THE INVENTION

A liquid crystal display device, which is referred to as a “lateralelectric field type”, is constituted such that a pair of transparentsubstrates are arranged to face each other in an opposed manner with aliquid crystal being disposed therebetween, and pixel electrodes andcounter electrodes, which generate an electric field (lateral electricfield) parallel to the transparent substrate between the counterelectrode and the pixel electrode, are formed on each pixel region on aliquid-crystal side of one of such transparent substrates.

With respect to light which passes through the region between the pixelelectrode and the counter electrode, the quantity of light is controlledby driving the liquid crystal to which the above-mentioned electricfield is applied.

Such a liquid crystal display device is a known display device havingbroad viewing angle characteristics, whose display is not changed evenwhen viewed from a direction oblique to a display surface.

Heretofore, the above-mentioned pixel electrode and the above-mentionedcounter electrode have been formed of a conductive layer which preventsthe transmission of light therethrough. However, recently, a liquidcrystal display device has been developed which has a constitution inwhich counter electrodes formed of a transparent material are formed onthe whole pixel region, except for the periphery of the pixel region,and strip-like pixel electrodes, which extends in one direction and arearranged in parallel in the direction intersecting such one direction,are formed on the counter electrodes by way of an insulation film.

In the liquid crystal display device having the above-describedconstitution, a lateral electric field is generated between the pixelelectrode and the counter electrode so that the liquid crystal displaydevice can largely enhance the numerical aperture while stillmaintaining excellent broad viewing angle characteristics. Such atechnique is described in, for example, in SID (Society for InformationDisplay) 99 DIGEST: p 202 to p 205 or Japanese Laid-open PatentPublication 202356/1999.

SUMMARY OF THE INVENTION

Although liquid crystal display device can provide drastically improvedviewing angle characteristics and an enhanced numerical aperture byadopting the above-mentioned liquid crystal driving method of thelateral electric field type, this approach also brings about various newtechnical problems to be solved.

For example, with respect to the liquid crystal display device havingthe above-mentioned constitution, although there has been an attempt touse a so-called multi-domain method which provides regions where thetwisting directions of liquid crystal molecules become reverse to eachother in each pixel of the liquid crystal display device and offsets thedifference of coloring which is generated when the display region isviewed from the left and right directions, it has been found that theliquid crystal display device needs various improvements from theviewpoint of the display quality.

The present invention has been made in view of such considerations, andit is an object of the present invention to enhance the performance ofdisplay operation (driving performance of liquid crystal molecules) ofthe liquid crystal display device of the above-mentioned so-calledlateral electric field type and to improve the display quality of such aliquid crystal display device.

Typical examples of features and aspects of the novel liquid crystaldisplay device disclosed in the present application are summarized asfollows.

An example of the novel liquid crystal display device is characterizedin that a pixel electrode and a counter electrode, which are arranged byway of an insulation film, are formed on a pixel region at aliquid-crystal side of one of the transparent substrates which arearranged to face each other in an opposed manner by way of liquidcrystal, and an electric field having a component parallel to thetransparent substrates is generated between these electrodes. One of thepixel electrode and the counter electrode is constituted of atransparent electrode which is formed on a region disposed around theother electrode and is not superposed on the other electrode, and theinsulation film has a multi-layered structure (structure in which theinsulation films are laminated at least in two layers).

In the liquid crystal display device having such a constitution,although the pixel electrode and the counter electrode, which arearranged by way of the insulation film, form a capacitive element at aportion where these electrodes are superposed on each other, when thesuperposed area becomes large, the capacitive element takes a valuewhich exceeds a necessary value. Accordingly, by providing theinsulation film disposed between the pixel electrode and the counterelectrode with a multi-layered structure, it is possible to decrease thecapacitance value of the capacitive element to a desired value.

Another example of the novel liquid crystal display device ischaracterized in that a pixel electrode and a counter electrode, whichare arranged by way of an insulation film are formed on a rectangularpixel region at a liquid-crystal side of one transparent substrate of apair of transparent substrates which are arranged to face each other inan opposed manner by way of liquid crystal, and an electric field havinga component parallel to the transparent substrates is generated betweenthese electrodes. The counter electrode is constituted of a transparentelectrode which is formed on a region disposed around the pixelelectrode and not superposed on the pixel electrode, and the pixelelectrode comprises a plurality of electrodes which are arranged inparallel in the direction perpendicular to an extension direction of thepixel electrode. The plurality of electrodes consist of first electrodeshaving bent portions which change the extension direction and a secondelectrode which is extended linearly at least at a portion of aperiphery of the pixel region.

In the liquid crystal display device having such a constitution, withrespect to the pixel electrode, besides the first electrodes, the secondelectrode which is extended linearly is newly mounted on at least aportion of the periphery of the pixel region, that is, a portion (a deadspace) where a lateral electric field is hardly generated since thefirst electrodes have the bent portions, whereby the lateral electricfield is also generated between the second electrode and the counterelectrode. Accordingly, the generation of a dead space can be suppressedso that the pixel region can be substantially increased.

These and other objects, features and advantageous effects according tothe present invention will be more explicitly described by relating thedescription of the mode for carrying out the invention to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing one embodiment of a pixel region of aliquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view taken along a line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view taken along a line 3-3 of FIG. 1.

FIG. 4 is a cross-sectional view taken along a line 4-4 of FIG. 1.

FIG. 5 is a plan view showing an external appearance of a liquid crystaldisplay panel which is incorporated into the liquid crystal displaydevice according to the present invention.

FIG. 6 is a cross-sectional view showing the constitution of a sealmember which is provided for fixing respective transparent substrates ofthe liquid crystal display panel and for sealing liquid crystal in aspace defined by respective transparent substrates.

FIG. 7A is a top plan view and FIG. 7B is a cross-sectional view showingone embodiment of a gate signal terminal of the liquid crystal displaydevice according to the present invention.

FIG. 8A is a top plan view and FIG. 8B is a cross-sectional view showingone embodiment of a drain signal terminal of the liquid crystal displaydevice according to the present invention.

FIG. 9A is a top plan view and FIG. 9B is a cross-sectional view showingone embodiment of a counter voltage signal terminal of the liquidcrystal display device according to the present invention.

FIG. 10 is an equivalent circuit diagram showing one embodiment of theliquid crystal display device according to the present invention.

FIG. 11 is a timing chart showing one embodiment of the driving of theliquid crystal display device according to the present invention.

FIG. 12 is a plan view of the liquid crystal display device according tothe present invention in a state wherein external circuits are connectedto the liquid crystal display panel.

FIG. 13 is a flow chart showing one embodiment of a method offabrication of the liquid crystal display device according to thepresent invention.

FIG. 14 is a flow chart showing one embodiment of a method offabrication of the liquid crystal display device according to thepresent invention, wherein the flow chart illustrates steps which followthe steps illustrated in FIG. 13.

FIG. 15 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 16 is a cross-sectional view taken along a line 16-16 of FIG. 15.

FIG. 17 is a cross-sectional view taken along a line 17-17 of FIG. 15.

FIG. 18 is a cross-sectional view taken along a line 18-18 of FIG. 15.

FIG. 19 is a flow chart showing another embodiment of the method offabrication of the liquid crystal display device according to thepresent invention.

FIG. 20 is a flow chart showing another embodiment of the method offabrication of the liquid crystal display device according to thepresent invention, wherein the flow chart illustrates steps which followthe steps illustrated in FIG. 19.

FIG. 21 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 22 is a cross-sectional view taken along a line 22-22 of FIG. 21.

FIG. 23 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 24 is a cross-sectional view taken along a line 24-24 of FIG. 23.

FIG. 25 is a cross-sectional view taken along a line 25-25 of FIG. 23.

FIG. 26 is a cross-sectional view taken along a line 26-26 of FIG. 23.

FIG. 27 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 28 is a cross-sectional view taken along a line 28-28 of FIG. 27.

FIG. 29 is a cross-sectional view taken along a line 29-29 of FIG. 27.

FIG. 30 is a cross-sectional view taken along a line 30-30 of FIG. 27.

FIG. 31 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 32 is a cross-sectional view taken along a line 32-32 of FIG. 31.

FIG. 33 is a cross-sectional view taken along a line 33-33 of FIG. 31.

FIG. 34 is a cross-sectional view taken along a line 34-34 of FIG. 31.

FIG. 35 is a graph showing the characteristics of appliedvoltage-transmissivity of the liquid crystal display devices of theabove-mentioned respective embodiments.

FIG. 36 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 37 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 38 is a cross-sectional view taken along a line 38-38 of FIG. 37.

FIG. 39 is a cross-sectional view taken along a line 39-39 of FIG. 37.

FIG. 40 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 41 is a cross-sectional view taken along a line 41-41 of FIG. 40.

FIGS. 42A and 42B are diagrams showing another embodiment of the pixelregion of the liquid crystal display device according to the presentinvention.

FIG. 43 is a cross-sectional view showing another embodiment of thepixel region of the liquid crystal display device according to thepresent invention.

FIG. 44 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 45 is a cross-sectional view taken along a line 45-45 of FIG. 44.

FIG. 46 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 47 is a cross-sectional view taken along a line 47-47 of FIG. 46.

FIG. 48 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 49 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

FIG. 50 is a plan view showing another embodiment of the pixel region ofthe liquid crystal display device according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A liquid crystal display device according to the present invention willbe explained in more detail in conjunction with various embodimentshereinafter.

Embodiment 1

<<Constitution of Pixel>>

FIG. 1 is a plan view of a pixel region of a liquid crystal displaydevice (panel) according to the present invention as viewed from aliquid-crystal side of one transparent substrate of respectivetransparent substrates which are arranged to face each other in anopposed manner while sandwiching liquid crystal therebetween.

A cross-sectional view taken along a line 2-2 of FIG. 1 is shown in FIG.2, a cross-sectional view taken along a line 3-3 of FIG. 1 is shown inFIG. 3, and a cross-sectional view taken along a line 4-4 in FIG. 1 isshown in FIG. 4.

First of all, in FIG. 1, gate signal lines GL, which extend in the xdirection in the drawing and are arranged in parallel in the y directionin the drawing, are formed of chromium (Cr), for example. Rectangularregions are formed by these gate signal lines GL and drain signal linesDL, which will be explained later, and these regions constitute pixelregions.

In the pixel region, an electric field is generated between counterelectrodes CT and pixel electrodes PX, which counter electrodes CT areformed on the whole area of the pixel region except for the peripherythereof. The counter electrodes CT are formed of transparent conductivebodies, such as ITO1 (Indium-Tin-Oxide), for example.

With respect to the counter electrodes CT, a counter voltage signal lineCL, which is connected to the counter electrode CT, is formed such thatthe counter voltage signal line CL frames the whole area of theperiphery of the counter electrode CT, and the counter voltage signallines CL are integrally formed with counter voltage signal lines CL thatare formed in the same manner as the counter electrode CT on the leftand right pixel regions in the drawing (respective pixel regionsarranged along the gate signal lines GL).

In this case, the connection of both counter voltage signal lines CL inthe pixel regions is performed at upper portions and lower portions ofthe pixel regions, respectively. Such a connection is made to minimizeportions where the counter voltage signal line CL and the drain signalline DL, which will be explained later, are superposed, so as to reducethe capacitance generated between them.

The counter voltage signal lines CL are made of opaque material, such aschromium (Cr). In such a case, an electric field which functions as anoise is generated between the drain signal line DL and a peripheralportion of the counter electrode CT, which is disposed close to thedrain signal line DL, so that the light transmissivity of the liquidcrystal may not be obtained as desired. However, since such a portion isshielded from light due to the counter voltage signal line CL, thedrawback in terms of display quality can be resolved.

This implies that the drawback derived from the electric field (noise)which is generated between the gate signal line GL and a peripheralportion of the counter electrode CT, which is disposed close to the gatesignal line GL, also can be resolved.

Further, as mentioned above, by making the material of the countervoltage signal line CL equal to the material of the gate signal line GL,these signal lines can be formed in the same step so that any increasein man-hours for fabricating can be obviated.

Here, it is needless to say that the above-mentioned counter voltagesignal lines CL are not limited to Cr and may be formed of, for example,Al or a material containing Al. However, in this case, it is moreadvantageous to position the counter voltage signal line CL as an upperlayer with respect to the counter electrode CT. This is because aselective etchant (for example, HBr) for an ITO film which constitutesthe counter electrode CT easily dissolves Al.

Further, it is advantageous to interpose a metal of a high meltingpoint, such as Ti, Cr, Mo, Ta, W, at least on a contact surface betweenthe counter voltage signal line CL and the counter electrode CT. This isbecause ITO, which constitutes the counter electrode CT, oxidizes Al inthe counter voltage signal line CL, thus forming a high resistancelayer. Accordingly, in one embodiment, when the counter voltage signallines CL are formed of Al or a material containing Al, it is preferableto adopt a multi-layered structure which uses the above-mentioned metalof a high melting point as a first layer.

Then, on an upper surface of the transparent substrate on which thecounter electrodes CT, the counter voltage signal lines CL and the gatesignal lines GL are formed, an insulation film GI, which is made of SiN,for example, is formed such that the insulation film GI covers them.

The insulation film GI functions as an interlayer insulation film of thecounter voltage signal lines CL and the gate signal lines GL withrespect to the drain signals DL, functions as a gate insulation film inregions where thin film transistors TFT are formed, and functions as adielectric film in regions where capacitive elements Cstg are formed.

Then, a thin film transistor TFT is formed in a superposed manner on aportion (left lower portion in the drawing) of the gate signal line GL,and a semiconductor layer AS, which is made of a-Si, for example, isformed on the insulation film GI at the portion.

By forming a source electrode SD1 and a drain electrode SD2 on an uppersurface of the semiconductor layer AS, a MIS type transistor having aninverse stagger structure, which uses a portion of the gate signal lineGL as a gate electrode, is formed. Here, the source electrode SD1 andthe drain electrode SD2 are simultaneously formed with the drain signalline DL.

That is, the drain signal lines DL, which extend in the y direction andare arranged in parallel in the x direction in FIG. 1, are formed, andportions of these drain signal lines DL extend over the surface of thesemiconductor layer AS so as to form the drain electrodes SD2 of thethin film transistors TFT.

Further, the source electrodes SD1 are formed at the time of forming thedrain signal lines DL, and these source electrodes SD1 also extend tothe inside of the pixel region so as to integrally form contact portionswhich serve to connect the source electrodes SD1 with pixel electrodesPX.

Here, as shown in FIG. 3, a contact layer d0 doped with n-type impurity,for example, is formed on interfaces between the semiconductor layer ASand the above-mentioned source electrode SD1 and the drain electrodeSD2. The contact layer d0 is formed such that an n-type impurity dopinglayer is formed on the whole area of the surface of the semiconductorlayer AS, the source electrode SD1 and the drain electrode SD2 areformed, and thereafter, using these respective electrodes as masks, then-type impurity doping layer formed on the surface of the semiconductorlayer AS, which is exposed from respective electrodes, is etched.

In this embodiment, the semiconductor layer AS is formed not only on theregion where the thin film transistor TFT is formed, but also onportions where the gate signal lines GL and the counter voltage signallines CL intersect the drain signal lines DL. Such a provision is madeto strengthen the function of the semiconductor layer AS as theinterlayer insulation film.

On the surface of the transparent substrate on which the thin filmtransistors TFT are formed in this manner, a protective film PSV, whichis made of SiN, for example, is formed such that the protective film PSValso covers the thin film transistors TFT. The protective film PSV isprovided for avoiding the direct contact of the thin film transistorsTFT with the liquid crystal LC.

Further, on an upper surface of the protective film PSV, pixelelectrodes PX are formed using transparent conductive films made of ITO2(Indium-Tin-Oxide), for example. The pixel electrodes PX are superposedon the regions where the above-mentioned counter electrode CT is formed.In this embodiment, five pieces of pixel electrodes PX are formed andthese pixel electrodes PX are respectively extended in the y directionwhile being equally spaced apart from each other, wherein these pixelelectrodes PX are connected with each other at both ends thereof bymeans of layers made of the same material which are respectivelyextended in the x direction.

In this embodiment, the distance L between the neighboring pixelelectrodes PX is set to a value in a range of 1 to 15 μm, for example,and the width W of the pixel electrode Px is set to a value in a rangeof 1 to 10 μm, for example.

Here, the material layers at lower ends of respective pixel electrodesPX are connected to contact portions of the source electrodes SD1 of theabove-mentioned thin film transistors TFT through contact holes formedin the protective film PSV, while the material layers at upper ends ofrespective pixel electrodes PX are formed in a superposed manner on theabove-mentioned counter voltage signal lines CL.

Due to such a constitution, at portions where the counter electrode CTand respective pixel electrodes PX are superposed, capacitive elementsCstg, which use the lamination film formed of the insulation film GI andthe protective film PSV as the dielectric film, are formed.

The capacitive elements Cstg are provided for storing video signals inthe pixel electrodes PX for a relatively long time even if the thin filmtransistor TFT is turned off after the video signals from the drainsignal line DL are applied to the pixel electrode PX through the thinfilm transistor TFT.

Here, the capacitance of the capacitive element Cstg is proportional tothe superposed area between the counter electrode CT and each pixelelectrode PX, and hence, there is a fear that the area is increasedrelatively and is set to a value which exceeds a necessary value.However, since the dielectric film adopts the laminated structure formedof the insulation film GI and the protective film PSV, there is no fearof such an eventually.

That is, since the insulation film GI serves as the gate insulation filmof the thin film transistor TFT, the film thickness can not beincreased. However, there is no such a restriction with respect to theprotective film psv. Accordingly, by setting the protective film PSV toa given film thickness (film thickness of only the protective film PSVbeing 100 nm to 4 μm, for example) together with the insulation film GI,it is possible to reduce the capacitance of the capacitive element Cstgto a given value.

It is needless to say that the protective film PSV is not limited toSiN, and the protective film PSV may be formed of synthetic resin, forexample. In this case, since the protective film PSV is formed bycoating, it is possible to obtain an advantageous effect in that, evenwhen the film thickness is to be increased, the fabricating isfacilitated.

Then, on the surface of the transparent substrate on which the pixelelectrodes PX and the counter electrodes CT are formed in this manner,an orientation film ORI1 is formed such that the orientation film ORI1also covers the pixel electrode PX and the counter electrodes CT. Theorientation film ORI1 is a film which is directly brought into contactwith the liquid crystal LC and determines the initial orientationdirection of the liquid crystal LC.

Although the pixel electrodes PX are constituted as transparentelectrodes in the above-mentioned embodiments, the pixel electrodes PXare not always transparent and may be formed of an opaque metalmaterial, such as Cr. This is because, although the numerical apertureis slightly decreased in such a case, this gives rise to no problem atall with respect to the driving of the liquid crystal LC.

Although the use of chromium (Cr) for the gate signal lines GL, thecounter voltage signal lines CL and the drain signal lines DL has beenproposed in the above-mentioned embodiments, it is needless to say thatother metal of a high melting point, such as Mo, W, Ti, Ta or an alloyof two or more kinds of these metals or a lamination film of two or morekinds of these metals or alloys, can be used.

Further, with respect to the transparent conductive film, although theuse of ITO as the transparent conductive film has been proposed, it isneedless to say that a similar advantageous effect can be obtained byusing IZO (Indium-Zinc-Oxide).

<<Filter Substrate>>

The transparent substrate having such a constitution is referred to as aTFT substrate and the transparent substrate which is arranged to facethe TFT substrate in an opposed manner by way of the liquid crystal LCis referred to as a filter substrate.

With respect to the filter substrate, as shown in FIG. 2, on aliquid-crystal-side surface, first of all, a black matrix BM is formed,such that respective pixel regions are defined, and in opening portionsof the black matrix BM, which substantially define the pixel regions,filters FIL are formed such that the filters FIL cover the openingportions.

Then, an overcoat film OC, which is formed of a resin film, for example,is formed such that the overcoat film OC covers the black matrix BM andthe filters FIL, and an orientation film OR12 is formed on an uppersurface of the overcoat film.

<<Overall Constitution of Liquid Crystal Display Panel>>

FIG. 5 is an overall view of a liquid crystal display panel showing adisplay region AR which is constituted of a mass of respective pixelregions arranged in a matrix array.

The transparent substrate SUB2 is formed so as to be slightly smallerthan the transparent substrate SUB1, and the transparent substrate SUB2is arranged such that a right side and a lower side thereof as seen inthe drawing become substantially coplanar with corresponding sides ofthe transparent substrate SUB1.

Due to such a constitution, regions which are not covered with thetransparent substrate SUB2 are formed on the left side and the upperside of the transparent substrate SUB1, as seen in the drawing. On theseregions, gate signal terminals Tg, which are provided for supplyingscanning signals to respective gate signal lines GL, and drain signalterminals Td, which are provided for supplying video signals torespective drain signal lines DL, are respectively formed.

The transparent substrate SUB2 is fixed to the transparent substrateSUB1 by means of sealing material SL, which is formed on a periphery ofthe transparent substrate SUB2. This sealing material SL also functionsas a seal-in material which hermetically fills the liquid crystal LCbetween respective transparent substrates SUB1, SUB2.

FIG. 6 shows that the liquid crystal LC which is interposed betweenrespective transparent substrates SUB1, SUB2 is hermetically sealed bymeans of the sealing material SL. A liquid-crystal filling opening INJis formed in a portion (a middle right side in FIG. 5) of the sealingmaterial SL, and this liquid-crystal filling opening INJ is sealed by aliquid crystal sealing agent (not shown in the drawing) after the liquidcrystal is filled through the liquid crystal filling opening INJ.

<<Gate Signal Terminals>>

FIGS. 7A and 7B show the gate signal terminal GTM which is provided forsupplying scanning signals to each gate signal line GL, wherein FIG. 7Ais a plan view and FIG. 7B is a cross-sectional view taken along a lineB-B of FIG. 7A.

First of all, the gate signal terminal GTM, which is formed of the ITOfilm ITO1, for example, is formed on the transparent substrate SUB1. Thegate signal terminal GTM is simultaneously formed with the counterelectrode CT. The reason why the ITO film ITO1 is used as the materialof the gate signal terminal GTM is to make the generation ofelectrolytic corrosion difficult.

Then, the gate signal line GL is formed such that the gate signal lineGL covers the gate-signal-line-GL-side end portion of the gate signalterminal GTM. Further, the insulation film GI and the protective filmPSV are sequentially laminated, such that these films cover the gatesignal terminal GTM and the gate signal line GL, and a portion of thegate signal terminal GTM is exposed through openings formed in theprotective film PSV and the insulation film GI. Here, theabove-mentioned insulation film GI and protective film PSV are formed asextension portions thereof in the display region AR.

<<Drain Signal Terminals>>

FIGS. 8A and 8B show the drain signal terminal DTM, which is providedfor supplying video signals to each drain signal line DL, wherein FIG.8A is a plan view and FIG. 8B is a cross-sectional view taken along aline B-B of FIG. 8A.

First of all, the drain signal terminal DTM, which is formed on thetransparent substrate SUB1, is constituted of the ITO film ITO01, whichexhibits a reliable characteristic against electrolytic corrosion, andthe ITO film ITO1 is simultaneously formed with the counter electrodeCT.

Then, although the drain signal terminal DTM is connected with the drainsignal line DL, which is formed on the insulation film GI, a drawbackarises when the drain signal terminal DTM is connected with the drainsignal line DL by forming the contact hole in the insulation film GI.That is, the insulation film GI made of SiN, which is formed on the ITOfilm, becomes a whitely muddy state at a portion thereof which isbrought into contact with the ITO film, so that when the contact hole isformed in the portion, the contact hole is formed in aninversely-tapered shape, whereby there still remains a possibility thatthe connection of the drain signal line DL becomes defective.

Accordingly, as shown in the drawing, a metal layer gI made of Cr, forexample, is formed on an end portion of the drain signal terminal DTM ina superposed manner, and the contact hole is formed on the insulationfilm GI formed on the metal layer gI.

Then, in forming the contact hole, the man-hours for fabricating aredecreased by forming the contact hole after forming the protective filmPSV on the insulation film GI. Accordingly, the drain signal line DL andthe metal layer gI are connected through the ITO film ITO2, which isformed simultaneously with the pixel electrode PX through the contacthole formed in the protective film PSV.

Here, the case in which Cr is used as the metal layer gI is shown,however the metal layer gI may be made of Al or a material whichcontains Al. In this case, since the metal layer gI is liable to beoxidized on a contact surface with the ITO film as mentioned above, itis possible to obtain a favorable connection by making the metal layergI have a three-layered structure which forms metal layers of a highmelting point on upper and lower surfaces of the metal layer gI, such asTi/Al/Ti.

<<Counter Voltage Signal Terminals>>

FIGS. 9A and 9B show the counter voltage signal terminal CTM, which isprovided for supplying counter voltage signals to the counter voltagesignal lines CL, wherein FIG. 9A is a plan view and FIG. 9B is across-sectional view taken along a line B-B of FIG. 9A.

The counter voltage signal terminal CTM, which is formed on thetransparent substrate SUB1, is also formed of the ITO film ITO1 havingreliable characteristics against electrolytic corrosion and issimultaneously formed with the counter electrode CT.

Then, the counter voltage signal lines CL are formed such that thecounter voltage signal line CL cover the counter voltage signal terminalCTM at a counter-voltage-signal-line-CL-side end portion. Further, theinsulation film GI and the protective film PSV, which are formed as theextension portions in the display region AR, are sequentially laminatedon these signal lines so as to cover these signal lines, and a portionof the counter voltage signal terminal CTM is exposed through openingsformed in the protective film PSV and the insulation film GI.

<<Equivalent Circuit>>

FIG. 10 shows an equivalent circuit of a liquid crystal display panelalong with exteriorly mounted circuits of the liquid crystal displaypanel.

In FIG. 10, scanning signals (voltage signals) are sequentially suppliedto respective gate signal lines GL, which extends in the x direction andare arranged in parallel in the y direction, from a vertical scanningcircuit V.

Thin film transistors TFT of respective pixel regions which are arrangedalong the gate signal lines GL to which the scanning signals aresupplied, are turned on by the scanning signals.

Video signals are supplied from a video signal driver circuit H torespective drain signal lines DL at the timing which matches the aboveoperation and the video signals are applied to the pixel electrodes PXthrough the thin film transistors of respective pixel regions.

In each pixel region, counter voltages are applied to the counterelectrode CT which is formed along with the pixel electrodes PX throughthe counter voltage signal line CL, so as to generate an electric fieldbetween them.

Then, the light transmissivity of the liquid crystal LC is controlled byan electric field (a lateral electric field) which has a componentparallel to the transparent substrate SUB1.

In the drawing, respective symbols R, G, B indicate respective pixelregions at which a red filter, a green filter and a blue filter arerespectively formed on respective pixel regions.

<<Timing Chart of Pixel Display>>

FIG. 11 is a timing chart of respective signals supplied to the liquidcrystal display panel. In the drawing, VG indicates the scanning signalsupplied to the gate signal line GL, VD indicates video signal suppliedto the drain signal line DL, and VC indicates the counter voltage signalsupplied to the counter voltage signal line CT. FIG. 11 is a drivewaveform diagram showing a general line inversion (a dot inversion) withthe potential of the counter voltage signal VC set at a fixed value.

<<Liquid Crystal Display Panel Module>>

FIG. 12 is a plan view which shows a module structure on which theexterior circuits are mounted on the liquid crystal display panel PNLshown in FIG. 5. In the drawing, to the periphery of the liquid crystaldisplay panel, the vertical scanning circuit V, the video signal drivercircuit H and a power supply circuit board PCB2 are connected.

The vertical scanning circuit V is constituted of a plurality of driverIC chips which are formed in a film carrier system, and output bumpsthereof are connected to the gate signal terminals GTM of the liquidcrystal display panel, while input bumps thereof are connected toterminals on a flexible substrate.

The video signal driver circuit H, in the same manner, is alsoconstituted of a plurality of driver IC chips which are formed in a filmcarrier system, and output bumps thereof are connected to the drainsignal terminals DTM of the liquid crystal display panel, while inputbumps thereof are connected to terminals on the flexible substrate.

The power supply circuit board PCB2 is connected to the video signaldriver circuit H through a flat cable FC, and the video signal drivercircuit H is connected to the vertical scanning circuit V through a flatcable FC.

The present invention is not limited to the above-mentionedconstitution, and it is needless to say that the present invention isapplicable to a so-called COG (Chip On Glass) system in whichsemiconductor chips which constitute respective circuits are directlymounted on the transparent substrate SUB1, and respective input andoutput bumps of the semiconductor chips are connected to terminals (orwiring layers) which are formed on the transparent substrate SUB1.

<<Fabricating Method>>

FIG. 13 and FIG. 14 are flow charts showing one embodiment of a methodof fabrication of the above-mentioned TFT substrate.

The fabrication is completed through photolithography steps (A) to (F).In respective drawings consisting of FIG. 13 and FIG. 14, the left sideindicates the pixel region and the right side indicates thedrain-signal-terminal forming region in the drawing.

Hereinafter, the fabricating method will be explained in the order ofthe steps thereof.

Step (A)

The transparent substrate SUB1 is prepared and an ITO film is formed onthe whole area of the surface thereof by sputtering, for example. Then,the ITO film is selectively etched by a photolithography technique so asto form the counter electrode CT on the pixel region and the drainsignal terminal DTM on the drain-signal-terminal forming region.

Step (B)

A Cr film is formed on the whole area of the surface of the transparentsubstrate SUB1. Then, the Cr film is selectively etched by aphotolithography technique so as to form the gate signal line GL and thecounter voltage signal line CL on the pixel region and the conductivelayer gi which constitutes an intermediate connector on thedrain-signal-terminal forming region.

Step (C)

A SiN film is formed on the whole area of the surface of the transparentsubstrate SUB1 by a CVD method, for example, thus forming the insulationfilm GI.

Further, an a-Si layer and an a-Si layer doped with n-type impurity aresequentially formed on the whole area of the surface of the insulationfilm GI by a CVD method, for example. Then, the a-Si layer isselectively etched using a photolithography technique so as to form thesemiconductor layer AS of the thin film transistor TFT on the pixelregion.

Step (D)

A Cr film is formed on the whole area of the surface of the transparentsubstrate SUB1 by a sputtering method, for example, and the Cr film isselectively etched by a photolithography technique so as to form thedrain signal line DL and the source electrode SD1 and the drainelectrode SD2 of the thin film transistor TFT on the pixel region andthe extension portions of the drain signal lines DL on thedrain-signal-terminal forming region.

Step (E)

A SiN film is formed on the whole area of the surface of the transparentsubstrate SUB1 by a CVD method, for example, thus forming the protectivefilm PSV. Then, the protective film PSV is selectively etched by aphotolithography technique so as to form the contact hole which exposesa portion of the drain electrode SD2 of the thin film transistor TFT onthe pixel region and the contact hole which penetrates the protectivefilm PSV and reaches the insulation film GI disposed below theprotective film PSV and exposes a portion of the conductive layer gI onthe drain-signal-terminal forming region.

Step (F)

An ITO film ITO2 is formed on the whole area of the surface of thetransparent substrate SUB1 by a sputtering method, for example. Then,the ITO film is selectively etched by a photolithography technique so asto form the pixel electrode PX which is connected to the drain electrodeSD2 of the thin film transistor TFT through the contact hole on thepixel region and the connection layer which connects the drain signalline DL and the above-mentioned conductive layer g1 on thedrain-signal-terminal forming region.

In the above-mentioned fabricating method, the step (A) and the step (B)can be reversed. That is, the counter electrode CT can be connected tothe gate signal line GL from above. In this case, it is necessary toform the cross-sectional shape of the gate signal line GL into a gentletapered shape.

On the other hand, in this system, since the counter electrodes CT aredisposed below the gate signal lines GL and the counter voltage signallines CL, a favorable connection can be obtained irrespective of thecross-sectional shape of the gate signal lines GL.

On the other hand, although the SiN film is used as the gate insulationfilm GI in this embodiment, the whitely muddy state of the ITO can besurely prevented, so that an insulation film containing oxygen, such asSiO₂ or SiON, may be used at least as the gate insulation film GI whichis brought into contact with ITO.

Embodiment 2

<<Constitution of Pixel>>

FIG. 15 is a plan view showing another embodiment of a liquid crystaldisplay device according to the present invention; and, FIG. 16, FIG. 17and FIG. 18 are respectively a cross-sectional view taken along a line16-16 of FIG. 15, a cross-sectional view taken along a line 17-17 ofFIG. 15 and a cross-sectional view taken along a line 18-18 of FIG. 15.

FIG. 15 corresponds to FIG. 1, which shows the embodiment 1, wherein thesame symbols as used in FIG. 1 indicate identical elements.

The constitution of this embodiment, which differs from the constitutionof the first embodiment, is that, first of all, counter electrodes CTwhich are formed of transparent electrodes, are formed on an insulationfilm GI, and the counter electrodes CT and the drain signal lines DL areformed on the same layer. This implies that the counter electrodes CTare formed as layers which are different from gate signal lines GL.Then, conductive films FGT, which are formed on a side portion of thecounter electrode CT at a position close to the drain signal lines DL,are formed on the same layer as the gate signal lines GL, wherein theconductive films FGT are formed such that the conductive films FGT arenot electrically connected with the counter electrodes CT.

Accordingly, as in the case of the embodiment 1, the conductive filmsFGT do not function as portions of the counter voltage signal lines CLand exclusively function as light shielding materials which prevent theleaking of light or the like due to liquid crystal derived from anelectric field generated between the drain signal lines DL and thecounter electrodes CT.

Such a constitution brings about an advantageous effect in that thedistance between the drain signal line DL and the counter electrode CTcan be narrowed, so that the numerical aperture can be enhanced.

However, it is needless to say that the conductive films FGT are notformed in such a manner and are formed on the same layer with thecounter electrodes CT, and they are formed such that the conductivefilms FGT are partially connected with side portions of the counterelectrode CT in the vicinity of the drain signal lines DL.

Then, in respective pixel regions, the counter electrodes CT ofrespective pixel regions, which are arranged along the drain signallines DL (in the direction perpendicular to the gate signal lines GL),are connected to each other. That is, the counter electrodes CT ofrespective pixel regions are integrally formed with each other astridethe region where the gate signal line GL is formed. In other words, thecounter electrodes CT of respective pixel regions, which are arrangedalong the drain signal lines DL, are formed in a strip shape along thedrain signal lines DL, and these respective strip-like counterelectrodes CT are divided by regions where the drain signal lines DL areformed.

These counter electrodes CT are formed on the layer different from thelayer for the gate signal lines GL, and hence, the counter electrodes CTcan be formed without being connected with the gate signal lines GL. Bysupplying counter voltage signals to the counter electrodes CT, whichare formed in such a strip shape, from the outside of a display region,which is formed as a mass of pixel regions, it is possible to obtain anadvantageous effect in that it is unnecessary to specifically form thecounter voltage signal lines CL shown in the embodiment 1.

Accordingly, by disposing the pixel electrodes PX closer to the gatesignal lines GL or by extending the pixel electrodes PX to an extentthat the pixel electrodes PX are superposed on the gate signal lines GL(see FIG. 15), it is possible to make the pixel electrodes PX have afunction of the pixel region also in the vicinity of the gate signallines GL. This brings about an advantageous effect in that, in thevicinity of the gate signal lines GL, it is sufficient to make the gatesignal lines GL per se have the function of the black matrix (in otherwords, the black matrix which covers the gate signal lines GL andportions in the vicinity of the gate signal lines GL being no morenecessary) so that the numerical aperture can be largely enhanced.

In the above-mentioned embodiment, among respective pixel regions, thecounter electrodes CT of respective pixel regions, which are arrangedalong the drain signal lines DL, are commonly constituted. However, itis needless to say that the counter electrodes CT of respective pixelregions which are arranged along the gate signal lines GL are alsocommonly constituted.

In this case, it is necessary that the counter electrodes CT are formedon a layer which is different from the layer for the drain lines DL, andit is applicable to the constitution of the embodiment 1.

<<Fabricating Method>>

FIG. 19 and FIG. 20 are flow charts showing one embodiment of the methodof fabrication of the liquid crystal display device described in theabove-mentioned embodiment. These drawings are similar to FIG. 13 andFIG. 14.

In comparison with the embodiment 1, this embodiment differs from theembodiment 1 in the fabrication steps corresponding to the difference inconstitution whereby the counter electrodes CT are formed on an uppersurface of the insulation film GI and the pixel electrodes PX are formedon the counter electrodes CT by way of the protective film PSV.

Embodiment 3

FIG. 21 is a plan view showing another embodiment of a liquid crystaldisplay device according to the present invention, and it is similar toFIG. 15. FIG. 22 is a cross-sectional view taken along a line 22-22 ofFIG. 21.

In FIG. 21, the same symbols as used in FIG. 15 indicate the same parts.

The portion of this embodiment which differs from the constitution shownin FIG. 15 is that, first of all, in the inside of respective pixelregions which are arranged along drain signal lines DL, counter voltagesignal lines CL, which run substantially in parallel with the drainsignal lines DL, are formed.

The counter voltage signal lines CL are formed right below (or mayberight above) counter electrodes CT. In other words, the counter voltagesignal lines CL are formed such that the counter voltage signal lines CLare connected to the counter voltages CT and have the function ofdecreasing the electric resistance of the counter electrodes CT per se.

The counter voltage signal lines CL are simultaneously formed with thedrain signal lines DL, for example, and are formed of the same materialas the drain signal lines DL. Accordingly, the counter voltage signallines CL are constituted of conductive layers having an electricresistance smaller than that of ITO, which constitutes the counterelectrodes CT.

The counter voltage signal line CL runs at the center of the pixelregion so as to divide the pixel region substantially in half. This isbecause the counter voltage signal line CL is formed such that theshort-circuiting of the counter voltage signal line CL and the drainsignal lines DL, which are disposed at both sides of the pixel region,can be surely avoided.

Further, the counter voltage signal line CL is formed in a superposedmanner on one of the pixel electrodes PX, which are formed such that thepixel electrodes PX extend in the y direction, as seen in the drawing.

In view of the fact that the portions on which the pixel electrodes PXare formed constitute portions which cannot avoid the reduction of thelight transmissivity, this embodiment is provided to minimize thereduction of the light transmissivity on the whole pixel region bypositioning the counter voltage signal line CL on the portion.

In this embodiment, the ITO film ITO1 is formed on an upper surface ofthe drain signal line DL by lamination and even when the drain signalline DL is formed in a disconnected state, the disconnection can berepaired by the ITO film ITO1.

Since the ITO film ITO1 can be simultaneously formed at the time offorming the counter electrode CT, it is possible to obtain anadvantageous effect in that the increase of man-hours for fabricationcan be avoided.

Embodiment 4

FIG. 23 is a plan view showing another embodiment of a liquid crystaldisplay device according to the present invention; and, FIG. 24, FIG. 25and FIG. 26 are respectively a cross-sectional view taken along a line24-24 of FIG. 23, a cross-sectional view taken along a line 25-25 ofFIG. 23 and a cross-sectional view taken along a line 26-26 of FIG. 23.

FIG. 23 is a view which is similar to FIG. 1, wherein symbols which arethe same as those used in FIG. 1 indicate the same parts.

The difference between the constitution of FIG. 23 and the constitutionof FIG. 1 is that pixel electrodes PX are formed on an insulation filmGI and counter electrodes CT are formed by way of the insulation filmGI. That is, the liquid-crystal-side pixel electrodes PX are arranged byway of a protective film PVS (and an orientation film ORI1).

Due to such a constitution, lines of electric force in the liquidcrystal LC are increased due to the voltage division effect derived fromthe protective film PVS, so that material having a low resistance can beselected as material of the liquid crystal LC, whereby it is possible toachieve an advantageous effect that the display with a small residualimage can be obtained.

Further, due to such a constitution, as shown in FIG. 25, a sourceelectrode SD1 of a thin film transistor TFT and the pixel electrode PXcan be directly connected; and, hence, the cumbersomeness of connectionthrough a contact hole formed in a protective film or the like, forexample, can be resolved.

Embodiment 5

FIG. 27 is a plan view showing another embodiment of a liquid crystaldisplay device according to the present invention; and, FIG. 28, FIG. 29and FIG. 30 are respectively a cross-sectional view taken along a line28-28 of FIG. 27, a cross-sectional view taken along a line 29-29 ofFIG. 27 and a cross-sectional view taken along a line 30-30 of FIG. 27.

FIG. 27 is similar to FIG. 1, wherein symbols which are the same asthose used in FIG. 1 indicate the same parts.

FIG. 27 shows a constitution which differs from the constitution shownin FIG. 1 in that, first of all, pixel electrodes PX are positioned aslower layers and counter electrodes CT are positioned as upper layers byway of an insulation layer.

As shown in FIG. 28, a first protective film PSV1 is formed on an uppersurface of an insulation film GI, and the pixel electrode PX is formedon the first protective film PSV1.

The pixel electrode PX is constituted of a transparent electrode whichis formed on a major portion excluding a periphery of the pixel region,wherein the pixel electrode Px is connected with a source electrode SD2of a thin film transistor TFT, which is formed as a layer below thefirst protective film PSV1 through a contact hole.

Then, a second protective film PSV2 is formed such that the secondprotective film PSV2 also covers the pixel electrode PX in such amanner, and the counter electrode CT is formed on an upper surface ofthe second protective film PSV2.

The counter electrodes CT is formed of a plurality of strip-likeelectrodes which extends in the y direction and are arranged in parallelin the x direction in the drawing in a region where the counterelectrode CT is superposed on the pixel electrode PX. These electrodesare formed such that the electrodes have the respective ends thereofconnected with conductive layers which are integrally formed withrespective counter electrodes CT over other whole areas, excludingregions between respective counter electrodes CT.

In other words, the counter electrodes CT are formed such that, amongthe conductive layers (ITO) which are formed so as to cover at least adisplay region, a plurality of strip-like openings, which extend in they direction and are arranged in the x direction in parallel in thedrawing, are formed in the conductive layers in the inside of regionswhich are superposed on the pixel electrodes PX.

This implies that conductive layers, other than the conductive layerswhich function as the counter electrodes CT, can be utilized as thecounter voltage signal lines CL. In this case, it is possible to obtainan advantageous effect in that the overall electric resistance of theconductive layers can be largely decreased.

Further, the conductive layers, other than the conductive layers whichfunction as the counter electrodes CT, can be formed in a state wherethe conductive layers cover the gate signal lines GL and the drainsignal lines DL. This implies that the conductive layers, other than theconductive layers which function as the counter electrodes CT, are givena function as a conventional black matrix layer.

An electric field (a lateral electric field) which has a componentparallel to a transparent substrate for controlling the lighttransmissivity of liquid crystal can be generated between the conductivelayer which functions as the counter electrode CT and the pixelelectrode PX and cannot be generated at portions other than theseportions.

Accordingly, as shown in FIG. 28, it is unnecessary to form the blackmatrix layer on the transparent substrate SUB2 side so that it ispossible to obtain an advantageous effect that man-hours for fabricationcan be decreased.

In this case, by adopting a so-called normally black liquid crystalwhich can generate a black display in a state in which an electric fieldis not applied to the liquid crystal, it is possible to strengthen thefunction of the conductive layer as a black matrix.

Further, it is inevitable that the gate signal lines GL or the drainsignal lines DL generate capacitance between these signal lines and theabove-mentioned conductive films. Accordingly, among the firstprotective film PSV1 and the second protective film PSV2, which areinterposed between these signal lines and the conductive films, byconstituting the second protective film PSV2, for example, using a resinfilm which can be formed by coating and by making such a resin film havea relatively large film thickness, the capacitance can be decreased. Forexample, when a SiN film having a relative dielectric constant of 7 anda film thickness of 100 to 900 nm is used as the first protective filmPSV1, it is proper to use an organic film having a relative dielectricconstant of 3 to 4 and a film thickness of 1000 to 3000 nm as the secondprotective film PSV2.

Further, when the relative dielectric constant of the second protectivefilm PSV2 is set to be equal to or less than ½ of the relativedielectric constant of the first protective film PSV1, it has beenconfirmed that no defects appear in practical products irrespective ofthe film thickness. Still further, when the film thickness of the secondprotective film PSV2 is set to twice or more of the film thickness ofthe first protective film PSV1, it has been confirmed that no defectsappear in practical products irrespective of the relative dielectricconstant.

Embodiment 6

FIG. 31 is a plan view showing another embodiment of a liquid crystaldisplay device according to the present invention, and FIG. 32 is across-sectional view taken along a line 32-32 of FIG. 31.

FIG. 31 shows a further improved constitution compared to theconstitution of the embodiment 5, and symbols which are the same as thesymbols used in FIG. 27 to FIG. 30 indicate identical elements.

The constitution of the embodiment 6 differs from that of the embodiment5 in that, first of all, pixel electrodes PX are formed on an insulationfilm GI and counter electrodes CT are formed on a first protective filmPSV1, which is formed on the pixel electrodes PX. In other words, thepixel electrodes px and the counter electrodes CT are formed ondifferent layers by way of the first protective film PSV1.

On the other hand, on other regions than the pixel regions, thesecond-protective film PSV2 is formed. The second protective film PSV2is formed such that, for example, the second protective film PSV2 isformed over the whole area of at least the display region, and,thereafter, portions thereof which correspond to the pixel regions areselectively etched.

Further, on a surface of the remaining second protective film PSV2, aconductive layer is formed. This conductive layer is integrally formedwith the counter electrodes CT. In the same manner as the fifthembodiment, the conductive film is formed on the whole area of at leastthe display region and, thereafter, in the conductive layer withinregions which are superposed on the pixel electrodes PX, a plurality ofstrip-like openings which extend in the y direction and are arranged inparallel in the x direction are formed, thus forming the counterelectrodes CT.

In the liquid crystal display device having such a constitution, it ispossible to obtain the following advantageous effects. That is, byinterposing the first protective film PSV1 and the second protectivefilm PSV2 between the gate signal lines GL or the drain signal lines DLand the above-mentioned conductive layer, the capacitance which isgenerated between the signal lines and the conductive layer can bedecreased, while by interposing only the first protective film PSV1between the pixel electrodes PX and the counter electrodes CT, anelectric field which is generated between them can be intensified at theliquid crystal LC side.

Comparison of Characteristics of Respective Embodiments

FIG. 35 is a graph which shows characteristics of transmissivityrelative to an applied voltage in respective constitutions of theabove-mentioned embodiment 1, embodiment 2, embodiment 4, embodiment 5and embodiment 6. Here, the liquid crystal display devices of respectiveembodiments are those which satisfy a so-called 15-type XGA Regulation,wherein the present invention is applied to devices whose width of gatesignal lines GL is set to 10 μm and whose width of drain signal lines DLis set to 8 μm.

In FIG. 35, for comparison purposes, besides the characteristics of theabove-mentioned embodiments, the characteristics of a TN-type TFT-LCDand an IPS-type TFT-LCD are also shown. From FIG. 35, it has beenconfirmed that the numerical aperture becomes 60% in the embodiment 1,the numerical aperture becomes 70% in the embodiment 2, the numericalaperture becomes 50% in the embodiment 4, and the numerical aperturebecomes 80% in the embodiments 5 and 6.

The reason why the embodiments 5 and 6 exhibit particularly highnumerical apertures is that these embodiments adopt the constitutionswhich make the black matrix, which has been conventionally used,unnecessary. Further, the reason why the embodiment 6 has a lowerdriving voltage compared to the embodiment 5 is that the embodiment 6adopts the constitution in which the second protective film PSV2 is notformed in the pixel region.

The above-mentioned characteristics are those of elements which areprepared by using liquid crystal material having mainly negativedielectric anisotropy. On the other hand, when liquid crystal materialhaving a positive dielectric anisotropy is used, although the maximumvalues of transmissivity of respective embodiments were decreased by0.5% respectively, an advantageous effect is obtained in that athreshold value voltage is reduced by 0.5 V.

Embodiment 7

FIG. 36 is a plan view showing another embodiment of the liquid crystaldisplay device according to the present invention for a case in whichthe above-mentioned respective embodiments are applied to a so-calledmulti-domain system liquid crystal display device. Here, with respect tothe multi-domain system, in an electric field (a lateral electric field)which is generated in the spreading direction of the liquid crystal,regions which differ in the direction of the lateral electric field areformed in the inside of each pixel region and by making the twistingdirection of molecules of the liquid crystal in each region opposite toeach other, an advantageous effect is obtained in that the coloringdifference which is generated when the display region is viewed from theleft and the right can be offset.

FIG. 36 constitutes a view which corresponds to FIG. 1, for example. Inthe drawing, respective strip-like pixel electrodes PX, which extend inone direction and are arranged in parallel in the direction whichintersects said one direction, are extended while being inclined withrespect to the above-mentioned one direction by an angle θ(appropriately 5-400 when the liquid crystal is P-type liquid crystaland the rubbing direction of the orientation film is aligned with thedirection of the drain signal lines); and, thereafter, respective pixelelectrodes PX are bent by an angle (−2θ) and are extended, and the aboveextensions are repeated, thus forming respective pixel electrodes PX ina zigzag shape.

In this case, by forming the counter electrode CT in a region of thepixel region excluding a periphery of the pixel region and by onlyarranging respective pixel electrodes PX having the above-mentionedconstitution to be superposed on the counter electrode CT, it ispossible to obtain the advantageous effect of the multi-domain system.

Particularly, it has been confirmed that the electric field which isgenerated between the counter electrode CT and the pixel electrode PX atbent portions of the pixel electrodes PX is generated exactly in thesame manner between the counter electrodes CT and the pixel electrode PXat other portions of the pixel electrodes PX. Conventionally, aso-called disclination region, which defines a non-transmitting portionwhere the twisting directions of molecules of the liquid crystal becomerandom, was generated.

Accordingly, it is possible to obtain an advantageous effect in that adrawback, whereby the light transmissivity is decreased in the vicinityof bent portions of the pixel electrodes PX, can be obviated.

Here, although the pixel electrodes PX are formed by extending them inthe y direction, as shown in FIG. 36 in this embodiment, the pixelelectrodes PX may be extended in the x direction in the drawing, andbent portions are provided to these pixel electrodes PX so as to obtainthe advantageous effect of the multi-domain system. Further, in thisembodiment, the advantageous effect of the multi-domain system isobtained by providing the bent portions to the pixel electrodes PX.

However, in the constitution wherein the pixel electrodes PX are formedat least on the whole area of the pixel region except for the peripheryof the pixel region, and, as shown in FIG. 28, for example, the counterelectrodes CT are extended in one direction and are arranged in parallelin the direction which intersects one direction, it is needless to saythat bent portions are provided to the counter electrodes so as toobtain the advantageous effect of the multi-domain system.

Embodiment 8

FIG. 37 is a plan view showing another embodiment of the liquid crystaldisplay device according to the present invention and constitutes a viewwhich is similar to FIG. 27.

Here, in FIG. 37, a cross-sectional view taken along a line 38-38 and across-sectional view taken along a line 39-39 are respectively shown asFIG. 38 and FIG. 39. Parts which are indicated by the same symbols asused in FIG. 27 are constituted of identical materials. The differencein constitution compared to FIG. 27 lies in the pixel electrodes PX.

The pixel electrode PX is constituted such that apertures are formed inportions which are superposed on the counter electrode CT whileexcluding a peripheral portion thereof. Accordingly, the center axes ofthe counter electrodes CT extending in one direction are substantiallyaligned with the center axes of the openings of the above-mentionedpixel electrode PX, wherein, assuming the width of the counter electrodeCT is W, the width of the opening is set to LL, which is smaller thanthe width W.

In such a constitution, the distribution of the electric field which isgenerated between the pixel electrode PX and the counter electrodes CTcan be generated exactly in the same manner as that of FIG. 27.

Accordingly, it is possible to obtain an advantageous effect in that, byforming the openings, the capacitance between the pixel electrode PX andthe counter electrodes CT can be decreased by an amount corresponding tothe openings.

As mentioned above, although the capacitance between the pixel electrodePX and the counter electrodes CT is necessary to some extent to storevideo signals supplied to the pixel electrode PX for a relatively longtime, when the capacitance is excessively increased, the brightnessirregularities of display derived from the delay of signals isgenerated. Accordingly, by giving the above-mentioned openings asuitable size, the capacitance can be set to an optimum value.

Here, in setting the value of capacitance generated between the pixelelectrode PX and the counter electrodes CT due to the openings formed inthe pixel electrode PX, there may be a case where a given capacitancevalue cannot be obtained due to the displacement of the counterelectrodes CT relative to the pixel electrode PX.

In this case, as shown in FIGS. 42A and 42B, for example, a pair of sideportions of the opening of the pixel electrode PX (in the drawing, thesides which are parallel in the y direction in the drawing being adoptedin view of the remarkable appearance of the drawback caused by thedisplacement) are formed in a zigzag shape, for example, so that anopening having crest portions (projecting portions) and valley portions(recessed portions) at respective sides is formed.

When the pixel electrode PX and the counter electrode CT are arrangedwithout the displacement as shown in FIG. 42A, the value of thecapacitance is determined by an area on which they are superposed. Then,even when the counter electrode CT is displaced in the x direction withrespect to the pixel electrode PX as shown in FIG. 42B, such asuperposed area is not changed, so that the value of capacitance is notchanged. This is because the relationship is established such that, whenthe crest portions of one side are retracted, the crest portions of theother side are projected.

It should be apparent that the pattern of the opening is not limited tothe above-mentioned pattern. For example, with respect to thedisplacement of one electrode, projecting portions which are projectedtowards the electrode side are formed on one of the sides of the openingwhich intersect the direction of displacement and projecting portionswhich are retracted with respect to the electrode are formed on theother side of the opening.

Such a constitution does not assume the constitution of FIG. 27, as apremise thereof, and is applicable to all of the above-mentionedrespective embodiments. For example, in the constitution where thecounter electrodes CT are formed on the whole area of the pixel region,except for the periphery of the pixel region, the openings may be formedin portions of the counter electrode CT which are superposed on thepixel electrode PX, except for the periphery of the counter electrodeCT. Further, although the openings of one electrode have the peripherythereof superposed on the other electrode, it is needless to say thatthe openings are not always interposed on the other electrode.

Embodiment 9

FIG. 40 is a plan view showing another embodiment of the liquid crystaldisplay device according to the present invention, and a cross-sectionalview taken along a line 41-41 is shown as FIG. 41.

FIG. 40 and FIG. 41 are views which illustrate an improvement of theembodiment 5 (FIG. 27-FIG. 30), wherein a characterizing point is that asecond protective film PSV2, which is constituted of a synthetic resinfilm, for example, serves as a spacer.

Here, the spacer consists of elements which support the othertransparent substrate with respect to one transparent substrate sidewhile maintaining an accurate gap and are required to make a layerthickness of liquid crystal uniform over the whole area of a displayregion.

In this embodiment, in regions are formed so as to be superposed onportions of gate signal lines GL, for example, regions where the spacersare formed, and the spacers are constituted as projecting portions whichare integrally formed with the second protective film PSV2.

By setting the locations where the spacers are formed at the same placesin respective pixel regions, it is possible to make the layer thicknessof the liquid crystal uniform over the whole area of the display region.This is because the spacers are provided at the same places, the laminarstructures of these portions become the same structure.

The spacers are formed such that, at the time of forming the secondprotective film PSV2, for example, first of all, a photosensitivesynthetic resin film is formed with a film thickness which adds a heightof the spacers, and, thereafter, light is selectively irradiated suchthat strong light is irradiated to the spacer forming regions and weaklight is irradiated to the regions, other than the spacer formingregions and then a developing step is performed.

With respect to respective spacers formed in this manner, the spacershaving the same height can be obtained with high accuracy so that it ispossible to maintain the gap between respective transparent substratesuniform over the whole area of the display region.

Although it is necessary to form the counter electrodes after thespacers are formed in this embodiment, even when material of the counterelectrodes remains on top surfaces of the spacers, since the electrodesare not arranged at the so-called filter substrate side, no drawback isderived from the constitution.

Further, although this embodiment is characterized as an improvement ofthe embodiment 5, it is needless to say that the present invention isnot limited to this embodiment.

This is because, when it is necessary to form a synthetic resin film asa layer which is disposed close to the liquid crystal, it is possible toobtain an advantageous effect in that the spacers can be formedintegrally with the synthetic resin film. Even when it is unnecessary toform such a synthetic resin film, the formation of spacers which arefixed to either one of the transparent substrates can make the gapbetween respective transparent substrates uniform with high accuracy.

Embodiment 10

FIG. 43 is a cross-sectional view showing another embodiment of theliquid crystal display device according to the present invention. FIG.43 shows a further improved constitution compared to the embodiment 5and is another cross-sectional view taken along a line 28-28 of FIG. 27.A planer view which shows a pixel region adopts the same constitution asFIG. 27 of the embodiment 5.

The difference in constitution compared to the embodiment 1 lies inthat, first of all, a protective insulation film PSV2, which is disposedbelow counter electrodes CT and separates pixel electrodes PX in aninsulating manner, is machined such that they are dug using counterelectrodes CT or counter voltage signal wirings CL as masks. Due to sucha machining, the insulation film PSV2 disposed between a drain signalline DL and the counter voltage signal line CL can be made thick and, inthe same manner, the insulation film on an area where the counterelectrode CT and the pixel electrode PX are directly superposed can beformed with a thick film thickness, while the insulation film PSV2 at adistance portion between the counter electrodes CT is formed with a thinfilm thickness.

As an advantageous effect of the above-mentioned machining, theinsulation film which is formed with a thick film thickness provides areduced capacitance as a load of the thin film transistor TFT or theload capacitance of the drain signal line DL can be reduced.

On the other hand, the insulation film PSV2 formed with a thin filmthickness results in a decrease in the voltage drop derived from theinsulation film between the pixel electrode PX and the counter electrodeCT, so that it is possible to supply a sufficient voltage to the liquidcrystal and a threshold voltage of the liquid crystal can be reduced.

Further, the machining of the insulation film PSV2 is performed usingthe counter electrodes CT as masks, and hence, the insulation film PSV2is machined in a self-aligned manner with the counter electrode CT sothat the display irregularities are hardly generated at all.

As can be clearly understood from the explanation with reference to theembodiments 1 to 10, according to the features of the present invention,a liquid crystal display device of extremely high performance can beobtained.

Embodiment 11

FIG. 44 is a plan view of a pixel region of another embodiment of theliquid crystal display device according to the present invention as seenby viewing one transparent substrate of a pair of transparent substrateswhich are arranged to face each other from the liquid crystal side byinterposing liquid crystal between them. Further, FIG. 45 is a viewshowing a cross section taken along a line 45-45 of FIG. 44.

First of all, in FIG. 44, gate signal lines GL, which extend in the xdirection and are arranged in parallel in the y direction in thedrawing, are formed on the transparent substrate SUB1 using chromium(Cr), for example. The gate signal lines GL form rectangular regionstogether with drain signal lines DL, which will be explained later, andthese regions constitute pixel regions.

In the pixel region, along with the gate signal line GL, a countervoltage signal line CL is formed, such that the connection of thecounter voltage signal line CL with the gate signal line GL and thesuperposition of the counter voltage signal line CL on the gate signalline GL and the drain signal line DL (formed in a later step) areavoided. Since the counter voltage signal line CL can be formed of thesame material as that of the gate signal line GL, the counter voltagesignal line CL is formed by the same step used for forming the gatesignal line GL. As shown in FIG. 44, the counter voltage signal line CLis constituted of a strip-like conductive layer CL′ which runs in the ydirection in the drawing at the center of the pixel region and aframe-like conductive layer CL″ which is connected with the conductivelayer and is formed along the periphery of the pixel region. Such acounter voltage signal line CL is connected with the counter voltagesignal lines CL in left and right pixel regions which interpose thispixel region through the counter voltage signal lines CL, which extendin the x direction. Although the counter voltage signal line CLfunctions as a signal line which supplies counter voltage signals to acounter electrode CT, which will be explained later, the counter voltagesignal line CL is also formed to function as a light shielding film. Thefunction of the counter voltage signal line CL as a light shielding filmwill be explained in detail later.

Further, over the whole area of a central portion of the pixel region,except for a trivial peripheral portion of the pixel region, the counterelectrode CT, which is made of ITO1 (Indium-Tin-Oxide), for example, andconstitutes a transparent conductor, is formed. In this embodiment andembodiments 12 to 15, which will be explained later, a profile of thecounter electrode CT (ITO1) which is formed of a transparent conductormounted on a substrate main surface side is depicted with a bold line.The counter electrode CT (ITO1) is partially covered with othertransparent conductor films (pixel electrodes PX (ITO2)) which aredisposed away from the main surface of the substrate. As the transparentconductor, in place of ITO used in this embodiment, a conductive filmwhich is formed such that the film can irradiate an incident light witha sufficient intensity (for example, a film which is capable oftransmitting at least 60% of an incident light), such as a metal thinfilm made of IZO (Indium-Zinc-Oxide) or formed by ion coating, forexample, may be used.

The counter electrode CT is formed such that a peripheral portion of thecounter electrode CT is directly superposed on an inner peripheralportion of the frame-like conductive layer of the above-mentionedcounter voltage signal line CL. Due to such a constitution, the countervoltage supplied from the counter voltage signal line CL is applied tothe counter electrode CT. An insulation film GI, which is made of SiN,for example, is formed on the whole area of an upper surface of thetransparent substrate SUB1 such that the insulation film GI also coversthe gate signal lines GL, the counter voltage signal lines CL and thecounter electrodes CT. The insulation film GI is configured to functionas an interlayer insulation film between the counter voltage signallines CL and the gate signal lines GL with respect to the drain signalline DL, which will be explained later, to function as a gate insulationfilm of the thin film transistors TFT, which will be described later, inregions where the thin film transistors TFT are formed, and to functionas a dielectric film in regions in which capacitive elements Cstg, whichwill be described later, are formed.

As shown at a left lower portion of FIG. 44, on the above-mentionedinsulation film GI at a portion of the thin film transistor TFT which ispartially superposed on the gate signal line GL, a semiconductor layerAS made of a-Si, for example, is formed.

By forming a source electrode SD2 and a drain electrode SD1 on an uppersurface of the semiconductor layer AS, an MIS-type transistor having aninverse stagger structure, which uses a portion of the gate signal lineGL as the gate electrode, is formed. Then, the source electrode SD2 andthe drain electrode SD1 are formed simultaneously with the drain signalline DL.

That is, the drain signal lines DL, which extend in the y direction andare arranged in parallel in the x direction in FIG. 44, are formed, anda portion of the drain signal line DL is extended over a surface of theabove-mentioned semiconductor layer AS so as to constitute the drainelectrode SD1 of the thin film transistor TFT.

Further, at the time of forming the drain signal lines DL, the sourceelectrodes SD2 are formed, and these source electrodes SD2 are extendedover portions in the inside of the pixel regions, so that contactportions which connect the source electrodes SD2 and the pixelelectrodes PX, which will be explained later, are integrally formed withthe source electrodes SD2.

Here, on an interface between the above-mentioned source electrode SD2and drain electrode SD1 of the semiconductor layer AS, contact layers dOwhich are doped with n-type impurity, for example, are formed. Thecontact layers dO are formed such that an n-type impurity doping layeris formed on the whole area of the surface of the semiconductor layerAS, the source electrode SD2 and the drain electrode SD1 are formed;and, thereafter, by using the respective electrodes as masks, the n-typeimpurity doping layer on the surface of the semiconductor layer AS,which is exposed from these respective electrodes, is etched.

Here, in this embodiment, the semiconductor layers AS are formed notonly in the regions where the thin film transistors TET are formed, butalso at portions where the gate signal lines GL and the counter voltagesignal lines CL intersect each other with respect to the drain signallines DL. This constitution is provided for strengthening the functionof the semiconductor layers AS as an interlayer insulation film.

Then, on the surface of the transparent substrate SUB1 on which the thinfilm transistors TFT are formed, a protective film PSV made of SiN, forexample, is formed such that the protective film PSV also covers thethin film transistors TFT. The protective film PSV is provided foravoiding direct contact of the thin film transistors TFT with the liquidcrystal LC.

Further, on an upper surface of the protective film PSV, pixelelectrodes PX, which are formed of transparent conductive films made ofITO (Indium-Tin-Oxide), for example, are formed. The pixel electrode PXhas a portion thereof connected to an extension portion of the sourceelectrode SD2 of the thin film transistor TFT through a contact holeformed in the above-mentioned protective film PSV.

The pixel electrode PX is constituted of a plurality of first electrodesPX′ having bent portions on the counter voltage signal line CL′, whichextends in the y direction, as seen in the drawing, at substantially thecentral portion of the pixel region and a frame-like second electrodePX” which respectively connects respective ends of these firstelectrodes PX′. In other words, these electrodes are configured suchthat the first electrodes PX′ are arranged at an equal distance in the ydirection, as seen in the drawing having an inclination of (−0:θ<45°)with respect to the counter electrode signal line CL′ in one pixelregion side defined by the counter electrode signal line CL′; and, thefirst electrodes PX′ are arranged at an equal distance in the ydirection, as seen in FIG. 44, having an inclination of (+0:θ<45°) withrespect to the counter electrode signal line in the other pixel regionside, and corresponding electrodes in respective pixel regions areconnected to each other on the counter electrode signal line CL′.

The provision of the bent portions to the first electrodes

means that the liquid crystal display device adopts the multi-domainsystem in which the directions of electric fields which the pixelelectrodes having one inclination (−0) and the pixel electrodes havingthe other inclination (+θ) respectively generate with respect to thecounter electrodes CT are different from each other, so that thetwisting directions of the liquid crystal molecules are opposite to eachother, whereby it is possible to obtain an advantageous effect in thatthe coloring difference which is generated when the display region isrespectively viewed from the left and right sides can be offset.

Respective bent portions of the first electrodes PX′ are positioned suchthat the bent portions are superposed on the signal line CL′, whichextends in the y direction at the center of the pixel region out of theabove-mentioned counter voltage signal line CL.

In the vicinity of bent portions of the first electrodes

the directions of the electric fields become random so that an opaqueregion (hereinafter this region is referred to as “disclination region”)is generated, to which a strict lateral electric field is not applied.Accordingly, this embodiment adopts the constitution which shields theregion from light by using the signal line CL′.

Further, with respect to the above-mentioned first electrode PX′, anopening angle of electrodes with respect to the bent portions as thecenter is set to 2θ (<90°), and hence, the opening angle assumes anacute angle.

In such a case, a relatively strong electric field is liable to begenerated between the first electrodes PX′ and the counter electrode CTat these bent portions so that the liquid crystal molecules are rotatedat a high speed. Accordingly, using these bent portions as startingpoints, a high-speed of rotation of the liquid crystal molecules can bepropagated to peripheries of the bent portions, as well as to the wholearea of the pixel region, whereby it is possible to obtain anadvantageous effect in that a display which can promote a rapid responseis achieved.

Further, out of the pixel electrodes PX, the second electrode PX″ isconstituted of a frame-like electrode PX″, which is superposed on theinner peripheral portion of the signal line CL″, which is formed in aframe-like shape out of the above-mentioned counter voltage signal lineCL. The second electrode PX” is connected with extending ends of theabove-mentioned first electrodes PX′.

Between portions of the second electrode PX″, which extends in the ydirection, as seen in FIG. 44, and the drain signal lines DL, which aredisposed adjacent to these portions, the above-mentioned counter voltagesignal lines CL″ are formed such that they extend in the y direction, asseen in the drawing.

The counter voltage signal lines CL″ are formed with a wide width, suchthat gaps between the drain signal lines DL and the counter voltagesignal lines CL″ can be made as small as possible. In other words, gapsformed between the electrodes PX″ which extend in the y direction, asseen in FIG. 44, out of the pixel electrodes PX, and the drain signallines DL, which are disposed adjacent to the electrodes PX″, areshielded from light by means of the counter voltage signal lines CL″.

Such a constitution is adopted for the following reasons. That is, anelectric field is generated from the drain signal line DL in response tovideo signals which are supplied to the drain signal line DL. Thiselectric field is terminated at the counter voltage signal line CL″ sideand the light transmission due to the change of the light transmissivityof liquid crystal, which is changed by the electric field, is shielded.

The pixel electrodes PX having such a constitution can achieve thefollowing advantageous effects.

First of all, since the regions, which differ in the directions ofelectric fields generated between the pixel electrodes PX and thecounter electrodes CT, are formed by dividing the pixel region intohalves, each pixel electrode PX (first pixel electrode PX′) has one bentportion, so that the total number of bent portions will become equal tothe number of the first pixel electrodes PX′.

In a conventional liquid crystal display device, for example, respectivepixel electrodes, which extend in the y direction and are arranged inparallel in the x direction, as seen in FIG. 44, are inclined on theright side along the longitudinal direction and then are inclined on theleft side along the longitudinal direction, and these inclinations arerepeated to form pixel electrodes having a zigzag shape. Compared tosuch a conventional liquid crystal display device, this embodiment canprovide a constitution which largely reduces the bent portions of theelectrodes. Accordingly, it is possible to largely reduce the generationof the disclination region at the bent portions of the electrodes PX′.

Further, by newly providing the second electrode PX″, which is arrangedin the frame shape in the periphery of the pixel region, besides theabove-mentioned first electrode PX′, the pixel electrode PX can generatea lateral electric field also between the second electrode PX″ and thecounter electrodes CT.

Conventionally, with respect to pixel electrodes having a zigzag shape,a small space and a large space are alternately formed between the pixelelectrode and the drain signal lines disposed close to the pixelelectrode; and, hence, so-called dead spaces where a sufficient lateralelectric field is not generated have been formed in the large spaces.Accordingly, by adopting the constitution of this embodiment, theabove-mentioned generation of the dead spaces can be suppressed so thatit is possible to achieve substantial enlargement of the pixel region.

Here, the second electrode PX″ also has a function of supplying videosignals to respective first electrodes PX′ through the source electrodeSD2 of the thin film transistor TFT. Accordingly, it is needless to saythat, so long as this function is satisfied, it is not always necessaryto form the second electrode PX″ in a frame-like shape along theperiphery of the pixel region.

For example, with respect to the second electrode PX″ of FIG. 44, evenwhen the upper-side (side opposite to the thin film transistor TFT)portion in the drawing, out of the portions extending in the x directionin parallel, as seen in the drawing, is not particularly formed, it ispossible to obtain a sufficient advantageous effect. On the surface ofthe transparent substrate SUB1 on which the pixel electrodes PX areformed in this manner, an orientation film (not shown in FIG. 44 andFIG. 45, see embodiment 1) is formed such that the orientation film alsocovers the pixel electrode PX. This orientation film is a film which issubjected to rubbing treatment in the y direction, as seen in thedrawing, and is brought into direct contact with a liquid crystal LC sothat the orientation film can determine the initial orientationdirection of the liquid crystal LC.

Although the pixel electrodes PX are constituted as transparentelectrodes in the above-mentioned embodiment, the pixel electrodes PXneed not always be transparent and may be formed of an opaque metalmaterial, such as Cr, for example. This is because, although thenumerical aperture is slightly decreased due to such a constitution,this gives rise to no defects in driving of the liquid crystal LC.

The transparent substrate SUB1 having such a constitution is referred toas a so-called TFT substrate, and the transparent substrate which isarranged to face this TFT substrate in an opposed manner whilesandwiching the liquid crystal LC therebetween is referred to as afilter substrate. On a liquid-crystal-side surface of the filtersubstrate, first of all, a black matrix is formed so as to definerespective pixel regions, and filters are formed such that the filterscover opening portions of the black matrix which substantially determinethe pixel regions. Then, an overcoat film made of a resin film, forexample, is formed such that the overcoat film covers the black matrixand the filters, and an orientation film is formed on an upper surfaceof the overcoat film. The details of these components are exactly assame as those described with reference to the embodiment 1.

Embodiment 12

FIG. 46 is a plan view which shows another embodiment of the liquidcrystal display device according to the present invention, and itconstitutes a view which corresponds to FIG. 1. Further, FIG. 47 is aview which shows a cross-section taken along a line 47-47 in FIG. 46.

This embodiment differs from the constitution shown in FIG. 44 in that,first of all, as a member which shields portions in the vicinity of bentportions of pixel electrodes PX having the bent portions from light, aconductive layer CL which is formed along with drain signal lines GL isused (accordingly, the conductive layer CL uses the same material as thesignal lines).

The conductive layer CL constitutes a counter voltage signal line LC;and, hence, a counter electrode CT, which is constituted of atransparent electrode, is formed in a superposed manner on an upperlayer (or on a lower layer if necessary) of the counter voltage signalline LC.

Further, since the conductive layer GL′ is formed such that theconductive layer GL′ runs in the y direction at the approximate centerof the pixel region, the conductive layer GL′ can be formed without anyfear of being short-circuited with respective drain signal lines GLwhich are positioned at both sides of the conductive layer GL′.

Embodiment 13

FIG. 48 is a plan view which shows another embodiment of the liquidcrystal display device according to the present invention, and itconstitutes a view which corresponds to FIG. 44.

The difference in constitution between this embodiment and theembodiment shown in FIG. 44 lies in the constitution of pixel electrodesPX, wherein, in place of portions of a frame-like second electrode PX″,to which respective end portions of a plurality of first electrodes

having bent portions are respectively connected and extend in the ydirection, as seen in the drawing, a third electrode PX3 is provided soas to extend in the y direction in the drawing, at the center portion ofthe pixel electrode.

Even when the liquid crystal display device is constituted in such amanner, it is possible to form the pixel electrodes over the whole areaof the pixel region without dead spaces.

Embodiment 14

FIG. 49 is a plan view showing another embodiment of the liquid crystaldisplay device according to the present invention, and it constitutes aview which corresponds to FIG. 44.

This embodiment differs from the embodiment of FIG. 44 in that the pixelregion is divided into halves to form regions which differ in thedirection of the electric field by a boundary which is parallel to the xdirection, as seen in the drawing.

Accordingly, this embodiment adopts a pattern in which pixel electrodesPX (first electrodes PX′) having bent portions are arranged with anangle of (−φ:φ>45°) with respect to the x direction, as seen in thedrawing, in one pixel region, and the pixel electrodes PX are arrangedwith an angle of (+φ:φ>45°) with respect to the x direction, as seen inthe drawing, in the other pixel region, and the corresponding pixelelectrodes are connected to each other at the boundary portion.

Even in such a case, it is possible to narrow the dead spaces and todecrease the number of the bent portions of the first electrodes PX′ ofthe pixel electrodes.

Further, in such a case, in view of the optimum setting of the initialorientation direction (the y direction in the drawing) of an orientationfilm and the directions of respective electric fields, the opening angle(2φ) at the bent portions of the first electrodes can be set to anobtuse angle. Accordingly, it is possible to decrease the generation ofso-called disclination regions at the bent portions of the pixelelectrodes (first electrodes).

As described above, in this embodiment, although light shielding meansare not provided to the bent portions of respective pixel electrodes, itis needless to say that light shielding means may be provided to achievethe complete prevention of generation of the disclination regions.

Here, it is needless to say that, in FIG. 49, with respect to the secondelectrode PX″, even when the upper side (the side opposite to the thinfilm transistor TFT) portion in the drawing among portions which arepositioned parallel to the x direction in the drawing is notparticularly formed, a sufficient advantageous effect can be obtained.

Embodiment 15

FIG. 50 is a plan view showing another embodiment of the liquid crystaldisplay device according to the present invention, and it constitutes aview corresponding to FIG. 44.

The difference between this embodiment and the embodiment of FIG. 44 inconstitution lies in the connection of a counter voltage signal line CLand the counter electrode CT. In this embodiment, gate signal lines GLuse a chromium (Cr) based alloy, wherein after forming the gate signallines GL on a substrate by patterning, the counter electrodes CT (ITO1)are formed before forming a gate insulation film GI made of SiNx. Forexample, in FIG. 13, the step (B) comes before the step (A) (the orderof the step (A) and the step (B) is reversed). ITO films whichconstitute the counter electrodes CT are directly brought into contactwith Cr films which constitute the counter voltage signal lines CL atthe centers of the pixels defined by openings of the black matrix BM(profiles thereof being indicated by broken lines).

In FIG. 50, the direction of an electric field which rotatably drivesliquid crystal molecules for modulating the light transmissivity of aliquid crystal layer, the direction of the electric field which isleaked from a drain signal line (also referred to as a video signalline, a data line) to the above-mentioned pixel (the region surroundedby a frame indicated by a broken line BM), and the advancing directionof a rubbing roller (so-called rubbing direction) at the time ofperforming the rubbing treatment on an orientation film (not shown inthe drawing) which covers the illustrated electrode structure arerespectively indicated by arrows of bold lines.

In this embodiment, the electric field which rotatably drives the liquidcrystal molecules is applied in the up-and-down direction of the drawing(the extension direction of the drain signal line DL). Accordingly, theinfluence which the electric field (lines of electric force) which isleaked from the drain signal line to the pixel in the left-and-rightdirection in the drawing gives to the rotation driving of the liquidcrystal molecules is reduced so that the degradation of the imagequality derived from longitudinal smear can be suppressed. The largerthe angle which is formed by the intersection of the direction of theelectric field which rotatably drives the liquid crystal molecules(arrow of “electric field applying direction to the liquid crystal”) andthe direction of the electric field which is leaked from the drainsignal line DL to the pixel (arrow indicating “electric field directionfrom the drain line”), the more efficiently the above-mentionedgeneration of longitudinal smear can be suppressed. When thisintersecting angle is small, it is necessary to shield the leaking ofthe electric field from the drain signal line DL to the pixel byproviding a counter electrode CT or a pixel electrode PX along the drainsignal line DL between the drain signal line DL and the pixel. However,in this embodiment, since the pixel electrodes PX (ITO2) which arearranged in a comb shape are arranged to intersect the drain line with asufficiently large angle, such a shielding structure is unnecessary.This feature is observed at a left upper portion and a right lowerportion of the pixel shown in FIG. 50 and serves to increase theaperture ratio of the pixel per se (area which can transmit lightmodulated by the rotation driving of the liquid crystal molecules).

Further, according to this embodiment, it is possible to increase thedegree of freedom of design of the electrode structure which isconstituted of the other transparent conductive film ITO2 (also referredto as “upper ITO layer” in view of the cross-sectional structurethereof), which is formed apart from one transparent conductive filmITO1, as viewed from a main surface of the substrate. Accordingly, it ispossible to design the whole pixel such that the voltage signalssupplied from the drain signal line DL can be applied to the pixelelectrodes PX along the line which intersects (preferably intersectingat a right angle) the extension direction of the drain signal line DL.

In this embodiment, since the extension direction of combs of the pixelelectrodes PX does not intersect the drain signal line DL at a rightangle, the rubbing direction (the liquid crystal molecules which are inthe state that the electric field is not applied to the liquid crystalmodules being oriented in the direction along this direction) can be setto a direction which intersects the drain signal line at a right angle.

In the above-mentioned embodiments 11 to 14, the counter electrode CT isformed such that the counter electrode CT extends over the whole area ofthe central portion of the pixel region, except for the trivialperiphery of the pixel region.

However, even when the counter electrode CT is not formed at portionswhich are superposed on the pixel electrodes PX, this does not exert anyinfluence on the operation of the liquid crystal. Accordingly, it isneedless to say that the counter electrode CT can be formed in thismanner.

Further, in the above-mentioned respective embodiments, the transparentelectrode which is formed over the whole area of the central portion ofthe pixel region, except for the trivial periphery of the pixel region,is formed as the counter electrode CT, and the electrodes provided withthe bent portions are formed as the pixel electrodes PX. However, thepresent invention is not limited to such a constitution. That is, it isneedless to say that the transparent electrode which extends over thewhole area of the central portion of the pixel electrode, except for thetrivial periphery of the pixel region, is formed as the pixel electrodePX, and the electrodes provided with the bent portions are formed as thecounter electrodes CT.

As can be clearly understood from the explanation which has been madewith reference to the embodiments 11 to 14, according to the liquidcrystal display device of the present invention, the display of imageshaving an excellent quality can be realized.

1. A liquid crystal display device comprising: first and second substrates with a liquid crystal layer therebetween; a plurality of gate signal lines made of metal and a plurality of drain signal lines made of metal, the gate signal line and the drain signal line have a first overlapping region; a plurality of counter voltage signal lines, the counter voltage signal line and the drain signal line have a second overlapping region; a plurality of pixel regions defined by neighboring gate signal lines and drain signal lines; and a pixel electrode formed on the first substrate in each pixel region; wherein a thin film transistor having a semiconductor layer is formed on the gate signal line; and wherein the semiconductor layer at least overlaps with the drain signal line at the first overlapping region and the second overlapping region.
 2. A liquid crystal display device according to claim 1, wherein a line width of the semiconductor layer is wider than a line width of the drain signal line at the first and the second overlapping regions.
 3. A liquid crystal display device according to claim 1, wherein a line width of the drain signal line at the first and second overlapping regions is narrower than a line width of the drain signal in major portions of the drain signal line other than at the first and the second overlapping regions.
 4. A liquid crystal display device according to claim 1, wherein a line width of the drain signal line at major portions of the drain signal line other than at the first and the second overlapping regions is wider than a line width of the semiconductor layer. 